Stainless steel has its characteristics of rust resistance, corrosion resistance and shining appearance, therefore, it is always preferred as the forming material of various metal products. Stainless steel casting, as its name implies, is the casting process of stainless steel alloys. Investment casting or lost wax casting, is the most precise casting method to manufacture stainless steel products, especially those irregular or complex structures, so stainless steel investment casting is almost equal to stainless steel precision casting. The whole casting stainless steel process contains several steps: mold making, wax model making, tree assembly, dipping and dewaxing, pouring, etc.
CFS Stainless Steel Foundry, located in Ningbo, China, has started its business of stainless steel investment casting since 30 years ago. In recent years, we continuously improve our production and management experience, and have become one of the largest stainless steel casting manufacturer and exporter in China. Currently, we can supply our customers all types of stainless steel castings with OEM services. To serve our customers better, value added services including heat treatment, post machining, surface finish are all available. We aim to supply our customers best quality, while competitive prices.
Common Cast Stainless Steel Grades
|304||Austenitic stainless steel with Ni content more than 8%, food grade alloy, can be used to cast stainless steel components for both household and commercial applications. It is the most widely used stainless steel casting material.304 stainless steel castings can be used in environments where the air is less corrosive.||Medical, food industry, chemical industry, mechanical equipment, pipe industry, automotive industry, etc.|
|316||Also austenitic stainless steel with Ni content more than 10%. For its higher Ni content, 316 stainlesss steel castings has better corrosion resistance than 304 stainless steel castings. Such stainless steel castings better suit for the marine environment with relatively harsh air conditions or chemical materials need to be contacted.||Fire fighting, auto parts, marine hardwares, chemical, pipeline, construction, decoration, food industry, etc.|
|304L / 316L||The mechanical properties are close to those of 304 and 316 materials. L represents lower carbon content, which makes the material more ductile, has good welding performance, and has more reliable corrosion resistance. The price is higher than that of materials of the same grade.||Food, chemical, medical, plumbing, etc.|
|410 & 416||Series 400 belongs to martensitic stainless steel, which is characterized by high strength, good processing performance and high heat treatment hardness, and does not contain Ni, so the corrosion resistance is weak.||Auto parts, tools, knives, etc.|
|17-4 PH||17-4 belongs to martensitic stainless steel with a Ni content of 3%-5% and good corrosion resistance. It has the highest strength in the stainless steel series and is usually used for products and components that are not prone to deformation.||Military, medical, mechanical components, machine tools, turbine blades, etc.|
|2205||Duplex stainless steel 2205 is a composite stainless steel consisting of 22% chromium, 2.5% molybdenum and 4.5% nickel-nitrogen.It has high strength, good impact toughness and good overall and local resistance to stress corrosion.||Sporting, pump & valve industry, etc.|
|304||≤0.08||≤1.00||≤2.00||≤0.03||≤0.045||18 ~ 20||8 ~ 11||–|
|304L||≤0.03||≤1.00||≤2.00||≤0.03||≤0.035||18 ~ 20||8 ~ 12||–|
|316||≤0.08||≤1.00||≤2.00||≤0.03||≤0.045||16 ~ 18||10 ~ 14||2 ~ 3|
|316L||≤0.03||≤1.00||≤2.00||≤0.03||≤0.045||16 ~ 18||10 ~ 14||2 ~ 3|
|410||≤0.03||≤1.00||≤1.00||≤0.03||≤0.040||11 ~ 13.5||≤0.6||–|
|416||≤0.15||≤1.00||≤1.25||≤0.15||≤0.060||12 ~ 14||≤0.6||–|
|17-4 ph||≤0.07||≤1.00||≤1.00||≤0.03||≤0.040||15.5 ~ 17.5||3 ~ 5||–|
|2205||≤0.03||≤1.00||≤2.00||≤0.03||≤0.040||21 ~ 24||4.5 ~ 6.5||2.5 ~ 3.5|
Stainless Steel Investment Casting Process
1. Wax Model Making & Assembly
Once the mold is ready, inject wax material into the mold cavity, then take out the wax model from the mold after cooling. Repair some appearance defects of wax models, such as slot, wax injection nozzle, flow pattern, etc. After inspection wax models, weld them to the casting system one by one to form a assembly, which looks like a tree.
2. Shell Building
Shell making process is a whole silica sol process, namely dip the assembly into good colloidal silica coating, sprinkle with fire-resistant sand, dry and harden shell under certain temperature,thus to form dense refractory coating surface outside the surface of wax models, and then repeat the step 5-6, finally form a certain strength and refractoriness of silica sol shell.
Dewaxing is a process in which the wax inside the shell is melted by high temperature steam and then drained out, resulting in a cavity that can be poured into the mold.
Melt stainless steel ingots into liquid status under a certain high temperature, then pour the liquid into the shell and cool under room temperature. After solidification, knock out the blacks and clean sand.
5. Cutting, Grinding & Surface Finishing
Cut the stainless steel casting blanks from assembly one by one, remove the sprue gate by grinding machine and smooth the surface by various surface finishes, such as shot blasting, sand blasting, electropolishing, mirror polishing, etc.
After finishing production, inspection is also an indispensable process before delivery. The inspection of stainless steel castings includes dimensional inspection, defects inspection and material inspection. Only qualified products can be shipped to customers.
Why Stainless Steel Casting? What Are The Benefits?
- Affordable Tooling: Tooling is the basic step to start stainless steel casting process. Although the machining accuracy and material of tooling plays an important role of the final casting quality, the tooling of stainless steel is relatively affordable compared with other forming processes.
- Flexible design: Investment casting can cast out stainless steel products in different sizes and weights, so the design of cast stainless steel parts is very flexible. Stainless steel casting allows parts with minimun 3mm thickness and weights ranging from 0.05kgs-80kgs. Besides, stainlesss steel castings with complex structures are also castable.
- Close Tolerance: The dimensional accuracy of stainless steel investment casting can meet ISO 8062 CT5-CT6 level. Such close tolerance can ensure stainless steel castings with less or no maching.
- Good Surface: Even after shot blasting, the surface of stainless steel castings is very smooth and looks bright. And people will never worry about stainless steel castings will get rust with the time flys.
- High Production Efficiency: Stainless steel casting is a fast and repeatable process, so the production efficiency is very high, and no matter it is large or small volume, it can all meet.
Heat Treatment: Solution Treatment
Solution treatment is a kind of heat treatment process in which stainless steel castings are heated to a high temperature and maintained constant temperature in the single-phase zone, so that the excess phase is fully dissolved into the solid solution and then cooled rapidly, so as to obtain the su-saturated solid solution. The purpose of solution treatment is mainly used to elimate the internal stress and improve the mechanical properties of cast stainless steel components, which will be easier to operate post machining.
Unlike heat treatment for other steel investment castings, solution treatment is the only heat treatment method used after stainless steel investment casting process. And we suggest heat treatment process especially for those stainless steel castings to be post machined, as the hardness of stainless steel castings is high, which is difficult to machine, and solution treatment will reduce the hardness effectively!
Investment casting is preferred to produce cast stainless steel parts mainly because it can creat near net shape products, even without secondary machining. But due to the limitations of stainless steel investment casting, this casting process can not creat net shape parts in most cases when there is a higher size accuracy and higher surface finish requirement. In this condition, post machining is operated to remove excess material by grinding, milling, drilling, etc. CNC machining is the most precise machining process, while the cost is high.
To serve our customers better, CFS has its machining capability to supply machined stainless steel castings for our customers when there is such requirement. With in house machining, we can do the inspection timely and solve problems in the shorest time. In addition, the machining cost is ideal compared with outsourced factory.
For stainless steel castings, there are several surface finish methods to improve its appearance, including shot blasting, sand blasting, electropolishing, mirror polishing, powder coating, etc.
Shot blasting: The most common and cost-optimal surface finish method to remove mill scales, burrs. It is the process to smooth stainless steel castings by the grinding of small steel balls in shot blasting machine.
Sand blasting: The process of cleaning the surface of stainless steel castings by the impact of high speed sand flow. The surface is more smooth than that of sand casting, while the cost is higher.
Electropolishing: A technique in which stainless steel castings are used as the anode for electrolysis in an appropriate electrolyte to selectively remove its rough surface and improve its surface smoothness. The surface is a bit shinning after electropolishing.
Mirror Polishing: Like its name, it is the manual polishing process operated with grinding wheel, and the surface will looks very shinning like a mirror, which is most time costing surface finish method. And due to its high requirement, the cost is highest compared with other surface finish ways.
Powder Coating: A surface treatment method for spraying plastic powder onto stainless steel castings. Like painting, there are different colors selected.
Stainless Steel Casting Applications
For metal castings requiring corrosion resistance and high strength, stainless steel casting is an ideal choice. The stainless steel investment casting process is used to create components for a range of industries including aerospace, petrochemical, medical, automotive, and food and dairy. Some of the parts and components commonly produced through stainless steel casting include:
- Valve bodies
- Marine equipment
- Medical devices