mim material stainless steel 17-4

MIM 17-4 PH Overview

Based on the AISI 17-4 PH standard, MIM 17-4 PH is a martensitic precipitation-hardening stainless steel. It is distinguished by a blend of corrosion resistance and mechanical qualities.

One of the most widely used MIM materials in the metal injection molding sector is 17-4 PH stainless steel. This metal has a great mix of corrosion resistance, hardness, and strength. Complex pieces with good strength are made possible by 17-4's exceptional qualities. Furthermore, secondary hardening is carried out during the sintering process by modifying certain parameters.

Since 17-4 PH resists corrosion similarly to 304L, it is frequently used in applications requiring mechanical properties.

Additionally, MIM-17-4 PH is identified by UNS S17400, AISI 630, ASTM A564, AMS 5643, and stainless steel 17-4 PH.

 

Composition of Chemicals

The chemical composition of Stainless Steel 17-4 is listed below, with elements and their respective weight percentages:

• Iron (Fe): Balance (remaining portion)
• Nickel (Ni): 3.00-5.00%
• Silicon (Si): 1.00%
• Carbon (C): 0.07%
• Chromium (Cr): 15.50-17.50%
• Niobium (Nb): 0.15-0.45%
• Manganese (Mn): 1.00%
• Copper (Cu): 3.00-5.00%
• Sulfur (S): 0.03%

The composition ensures the material's strength, corrosion resistance, and other properties suitable for various industrial applications.

MIM 17-4 PH stainless steel typically has mechanical qualities that are 10–25% worse than wrought 17-4 PH. The primary causes include:

Sintering flaws include lingering carbon impurities, retained pores, and grains.
Evaporation-induced loss of elements: Cr, Cu, and Ni.
Impurity inclusion: O, C, and N.

With slowing sintering, the face-centered cubic austenite phase is stabilized by carbon and nitrogen components. On the other hand, body-centered cubic delta ferrite will accelerate the pace of sintering. Stainless steel 17-4PH undergoes precipitation reactions that result in high hardness and strength, whereas residual delta-ferrite decreases strength. Additionally, martensite occurs during the cooling phase after sintering.

A key component of Mim Products is oxygen. The initial surface area of stainless steel powders coated with oxides is high, and the amount of oxygen varies depending on the powder manufacturing method. High oxygen levels in MIM 17-4 PH parts lead to poor corrosion resistance and inferior mechanical characteristics since these oxides will take away chromium's ability to inhibit corrosion.

 

The Typical Properties

A sophisticated technique for creating intricate, high-performance stainless steel parts is MIM. Peak temperature, heating rate, environment, holding duration, and powder particle size all affect how stainless steel 17-4 PH sinters. Numerous factors impact the composition of the 17-4 PH alloy, which in turn impacts the microstructure phases, sintering behavior, and ultimate characteristics. Nitrogen from the process atmosphere, oxygen from the powder or atmosphere, and carbon from the powder or binder are the primary components.

 

The ideal balance of strength, hardness, and corrosion resistance makes 17-4 PH a popular choice. Products in the fields of electronics, dentistry, medicine, and aerospace find the mix of qualities appealing after heat treatment. varying according to the composition, with changes in Fe, Ni, Cu, and Cr. The temperature of solidus is around 1405°C, and that of liquidus is approximately 1440°C. The mechanical qualities are responsive to heat treatment; fracture elongation ranges from 8 to 14%, yield strength ranges from 760 to 1240 MPa, tensile strength ranges from 1000 to 1340 MPa, and hardness reaches 43 HRC.

 

The exceptional combination of strength, hardness, and corrosion resistance makes 17-4 PH stainless steel a preferred choice in the metal injection molding industry. The martensitic stainless steel that is most commonly precipitation hardened is 17-4 PH.

• Great strength
• Extremely hard
• Superb resistance to corrosion
• Toughness for fractures
• characteristics of heat treatment and welding

 

Effects of Binder and Debinding

For stainless steel 17-4 PH injection molding, many binder systems are used; the most popular ones are 60% filler, 30% backbone, and 10% surfactant.

Because leftover binder ingredients will alter the final oxygen or carbon levels, debinding has an impact on the final characteristics. De-polymerization or solvent extraction is the initial step in debinding; for example, paraffin wax dissolves in heptane, and polythylene glycol dissolves in hot water. Moreover, fuming nitric acid is used in catalytic debinding to remove polyoxymethylene. The best way to remove the binder in the second stage of debinding is to hold it at 600 to 1000°C in a hydrogen environment. This phase is sometimes referred to as the sintering start stage.

 

Sintering Parameter Impact

A number of variables interact during the sintering of stainless steel 17-4 PH to define the final density, phase, microstructure, and characteristics. The four primary components of statistical analysis are heat treatment, sintering atmosphere, initial oxygen concentration, and particle size.

The sintering temperature has the most influence on sintered density.

 

The size of particles

Surface diffusion is the process by which the first particle bonding during sintering takes place; a smaller particle with a larger surface area will strengthen the initial bond. The backbone polymer's particle adhesion will be replaced by surface diffusion bonding once binder pyrolysis takes place. Grain boundary diffusion needs neck growth as sintering bonding between metal particles increases in order to create grain boundaries between particles. When the grain boundary forms, the grain size plays a major role in sintering when shrinkage begins, and it has an inverse effect on the sintering rate. However, the impact of initial particle size can be counteracted by greater peak temperatures or longer holding times.

 

The atmosphere

In stainless steel, the standard sintering environment options include vacuum, hydrogen, nitrogen, hydrogen-nitrogen, and argon-hydrogen.


The two most popular sintering atmospheres for stainless steel 17-4 PH are hydrogen and vacuum. There is a noticeable drop in oxide when carbon is added. Both silicon and chromium can hold onto oxygen without the carbon addition of graphite. Oxide reduction occurs when the temperature is high and the hydrogen level is high; a low dew point will guarantee this process. The cold surface oxidation that occurs after sintering will create a passive coating of silicon, iron, and chromium that resists corrosion.

As a strong austenite stabilizer, nitrogen has an impact on the development of martensite and the ultimate characteristics of stainless steel. As it cools, nitrogen, which is soluble in austenite, precipitates as Cr2N. The chromium in the grain boundary area will be depleted by this precipitate, which will cause localized corrosion to occur quickly. As a result, we must prevent nitrogen from entering the sintering atmosphere and cool the components below 900°C at a pace of 200°C per minute. in stainless steel 17-4 PH to prevent the production of chromium nitride.

Graphite also produces low partial pressures of carbon monoxide in vacuum furnaces, which is why graphite vacuum furnaces are successful in vacuum sintering. At 1300°C and a low CO partial pressure of 0.001, it can convert chromium oxide to chromium.

 

 

Temperature and Heating Rate

Typical sintering cycles include impurity elimination and binder burnout processes that entail heating and holding at various temperatures. For impurity reduction, the ideal temperature is close to 1000°C, while for ultimate polymer removal, it is close to 600°C.

Stainless steel 17-4PH undergoes sintering shrinkage in dilatometry testing at a peak rate of about 1250°C, whereas full-density (98%) necessitates a peak temperature of 1300°C. Copper and chromium will, however, evaporate at these high temperatures, perhaps causing a loss of heat treatment and corrosion resistance.

 

Additionally, the synthesis of delta-ferrite is aided by greater temperatures; by faster diffusion, this phase will aid in the final densification. White delta-ferrite colonies and dark areas of circular oxide pores are visible in the following micro-structure graph of MIM 17-4PH in sintering.

The microstructure of 1260 SS17-4 MIM

 

Control of Carbon

During the sintering process, carbon is another austenite stabilizer. Higher strength and hardness will be achieved with low retained carbon content levels in 17-4, below 0.1 weight percent. Stainless steel 17-4 PH's phases, densification, and mechanical characteristics will all be impacted by the carbon content change.

 

The MIM process's atomized powder, binder residues, debinding cycle, sintering environment, starting oxygen, and peak sintering temperature are some of the variables that affect the carbon level. The primary determinant of the ultimate carbon content during sintering is the initial oxygen level. For example, 0.03% carbon is lost during hydrogen sintering of 17-4 gas atomized powders at 1343°C. Furthermore, particularly at lower sintering temperatures, binder residues can also cause carbon contamination.

In hydrogen and vacuum sintering, the tensile strength of stainless steel 17-4 is influenced by the amounts of carbon that are retained. In either the H900 or H1100 heat treatment, or in the standard sintering at 1300 to 1360°C. The following image illustrates how tensile strength noticeably decreases as carbon content rises.

 

Maintaining Time

In sintering, holding times at the highest temperature fall between 60 and 120 minutes. from the sintered density versus temperature and time graph that follows. As the temperature rises from 1240°C to 1360°C, it shows a progressive density from 96.3% to 98.3%. The sintering compacts achieve full density (98%), after 60 minutes of holding. Porosity is removed and the rate of pore annihilation is decreased during this phase. The loss of grain boundaries and porosity fatigue are the primary causes.

 

Benefits of MIM 17-4

High resistance to corrosion
Heat treatment-induced age hardening
Industrial strength and durability
Outstanding resistance to heat
Ideal for MIM's complicated geometry

 

Mechanical Characteristics

As for structural devices, MIM 17-4 PH is used. Favorite comparable characteristics are strength, hardness, and elongation. In addition, fatigue, yield strength, and fracture toughness are issues that are impacted by several processing variables.

The following image summarizes the average parameters of 17-4 PH based on statistical analysis of several MIM projects. Sintering parameters are responsible for around 60% of the variation in properties.

 

According to the MIM industry standard, stainless steel 17-4 PH must have a minimum tensile strength of 790 MPa, a hardness of 27 HRC after sintering, and a hardness of 1070 MPa and 33 HRC after heat treating. 4% elongation for both. The tensile strength of stainless steel 17-4PH after 1350°C sintering and H900 heat treatment is 1280 MPa for gas-atomized powder and 1136 MPa for water-atomized powder. It should be noted that gas atomized powder can achieve a heat-treated tensile strength of 1485 MPa with 9% elongation.

 

Resistance to Corrosion

Four types of sintered stainless steel (304, 316, 430, and 17-4) are subjected to standard corrosion testing in a variety of situations. The results show that 17-4 is the least resistant to these conditions. Furthermore, because pores on sintered components cause local corrosion by concentration polarization, wrought material is more resistant to corrosion than sintered material. Hydrogen sintering and gas atomized powder are two popular techniques to improve corrosion resistance because residual oxygen is a drawback.

Corrosion resistance is also related to biocompatibility. When compared to titanium and cobalt alloys, stainless steel 17-4 PH has good cytotoxicity but lacks competitive overall biocompatibility.

 

PH Application Market for MIM 17-4

Outstanding mechanical qualities are provided by 17-4 PH stainless steel at temperatures as high as 350°C. In addition, it is durable enough for both vase metal and welds, and warping and scaling can be reduced by heating at a low temperature for a brief period.

Because of its superior corrosion and heat resistance, aerospace 17-4 stainless steel is a great choice for aerospace applications. High powder purity and densification can ensure the lifetime of MIM 17-4 products and minimize error change.

Vehicles
The most widely used material in the production of automobiles is stainless steel 17-4 because it is simple to process into a variety of shapes. With considerable durability, metal injection molding technology also increases its capacity for complex geometry.

Customers
Because of its exceptional corrosion resistance, 17-4 is widely used in consumer applications utilizing MIM technology. Furthermore, the exceptional strength and hardness of this material guarantee error-free functionality.

In conclusion

MIM 17-4 PH makes amazing strides in optimizing structural properties. For numerous appropriate applications, it offers a variety of appealing combinations of sintered properties. Sintering temperature is the primary determinant of final attributes when compared to powder type, particle size, green density, holding duration, and other parameters. Furthermore, the phase that is present in sintered materials affects the sintered properties.

In the meantime, post-sintering heat treatment, sintered density, and phase morphology all affect characteristics. While sintered density determines characteristics, Hot Isostatic Pressing (HIP) enhances them.

Metal Injection Molding (MIM) is becoming increasingly advanced with stainless steel 17-4 PH. To offer further applications for sintered 17-4 PH, JHMIM depends on the MIM technology base.