Mold-grade stainless steels are a subgroup of 420. These special grades have higher corrosion resistance and polishability, ideal for machined parts, plastic molding dies, and firearm components.

Stainless steels are commonly “aged,” a process also known as precipitation hardening. Precipitation hardened stainless steels such as 17-4 and 13-8Mo provide increased corrosion resistance and are ideal for service in high-heat environments. During the aging process, particles “precipitate” out of the intermetallic structure, thus allowing the material to harden—hence, why this process is called “precipitation hardening.”

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Case hardening, nitriding, and FNC are used to increase wear resistance in special applications where carburization is required. These processes work to break down the oxide layer that forms on the surface of stainless steel to let oxygen in to carburize the material effectively. All case hardening processes are used for the same reasons, but FNC lends the greatest degree of corrosion resistance in the finished parts. Martensitic and austenitic stainless steels can both be carburized; the only downside is that they can reduce the corrosion resistance of the stainless material.

Root sum square

The choice in tolerance analysis method is based on many factors, but the can be summarized as “Which method best matches the manufacturing and inspection process of the assembly”. For simple fit problems, a 1D stack-up may be sufficient. RSS is sufficient for the small number of scenarios where the inputs are normal and the assembly relationships are linear. For all other scenarios, Second Order Tolerance Analysis is required to address the real world of manufacturing.

RSS (Root-Sum Squared) Statistical Analysis does not focus on the extreme values, but focuses on the distribution of the variation for each dimension. Each dimension will have a unique distribution of values based on the manufacturing process. Tool wear, operator differences, changes in material and environment all contribute to variation in the dimension value. Each dimension has its own distribution curve.

Unlike most materials, stainless steel shrinks during the precipitation hardening process. The exact shrinkage rate depends on the steel grade, but it’s predictable. We typically observe a shrinkage rate from 0.0004–0.0008 inches per inch, depending on the length of the part.

Our tolerance analysis and GD&T solutions  unite the ideal world of product design with the real world of manufacturing and assembly—where mechanical variation has a significant impact on product cost.

Because manufacturing methods vary for different types of parts, the distribution moments or parameters change as well. RSS only uses standard deviation and does not include the higher moments of skewness and kurtosis that better characterize the effects tool wear, form aging and other typical manufacturing scenarios. Second Order Tolerance Analysis incorporates all distribution moments:

Martensitic stainless steels like 410, 416, 420, and 440C are generally the strongest grade of stainless steel available due to higher carbon content and less nickel than their austenitic counterparts.

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In a previous article, we discussed many factors that make stainless steel procurement risky, and there are also risks that come with heat treatment processes. To achieve the most predictable outcomes for your stainless steel parts, it’s best to consult the metallurgy experts on your heat treatment team. At Paulo, we often work with our customers to ensure part designs are optimized so that heat treatment yields finished parts that meet all required specifications for service in the field.At Paulo, we have a long history of working with stainless steel. We work closely with engineering teams and materials suppliers to help our customers deliver precise, reliable parts for automotive, aerospace, and beyond. Have questions about an upcoming stainless steel project? Request a quote or connect with a Paulo expert today.

In a Worst-Case Analysis, each dimension will have a minimum and maximum value that represents the range of acceptability for that dimension. Worst-Case answers the question, if I take the maximum range on each input, what is the maximum range for the measurement of interest or stackup? We are therefore dealing with the limits of acceptability and not probability.

Through hardening is commonly used on stainless steel springs, seating components, hand tools, and other parts that are required to sustain heavy loads.

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Second Order Tolerance Analysis is also needed to determine what your output is going to be when the assembly function is not linear. In typical mechanical engineering scenarios kinematic adjustments and other assembly behaviors result in non-linear assembly functions. Second order calculations are much more complex so hand calculations are not advisable but the computation accuracy is greatly improved and becomes viable within a tolerance analysis software package.

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Our systems are designed to integrate within the primary 3D cad environments in which manufacturers design parts and assemblies. Enabling them to utilize Geometric Dimensions & Tolerancing reporting to create efficient Tolerance Analysis and Variations for viable products.  Thus creating an early modeling method prior to production and assembly for increased ROI creating the need for a world renowned GD&T software. For more information the relationship of quality and profitability in manufacturing click here, or read through our white papers and case studies throughout the website.

Compared to austenitic and martensitic stainless steel, ferritic stainless is best suited for cost-conscious applications where components don’t require high durability or extreme temperature resistance. For example, car exhausts and bathroom fixtures are commonly made from ferritic stainless steel.

When you combine the probabilities for each dimension (each separate curve) you get the probability for the total and therefore the distribution curve of the total. Statistical analysis answers the question, given the distribution of variation on each dimension what is the probability that my performance characteristic will fall within defined acceptable limits. The limitation of RSS is that it assumes all inputs are normally distributed and all performance characteristics have a linear relationship with the dimension. These assumptions do not account for the breadth of conditions that exist in typical scenarios found in manufacturing.

The simplest form of tolerance analysis is the single direction, 1D Tolerance Stackup. A 1D Tolerance Stackup is created by creating a cross section of a model and adding the tolerance values for each feature in a straight line. The variation in each contributes to the overall output/outcome.

Martensitic and precipitation hardening-grade stainless steels can both be through hardened. Through hardening, or rapid quenching, is a process that involves heating an alloy to enhance its physical properties and quickly quenching to preserve those properties achieved during the heat treating process.

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Grade 440C is the ultimate tool steel stainless steel weighing in at 1% carbon and with a higher wear resistance than most steels. It’s mostly used in cases that require good corrosion and wear resistance, such as food processing. Industrial cutting and grinding tools are often made from 440C.

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The corrosion resistance of stainless steel, thanks to its greater chromium content, makes it an obvious choice for parts that require protection against oxidation. However, there are many different types of stainless steel, each offering different benefits. In this article, we’ll discuss the different grades, their limitations, and heat treating processes used to enhance material properties for varying applications.

A statistical tolerance analysis is when you take the variation of a set of inputs to calculate the expected variation of an output of interest. In mechanical engineering, a product design is composed of multiple features, each with tolerance values that control the variable aspects of those features. Statistical tolerance analysis is used to understand how these tolerances contribute the various performance characteristics of the design.

When cold forming, annealing is especially important. Stainless steel work hardens quickly when bent, and the material often needs to be annealed between forming operations to keep it workable. As we previously mentioned, annealing also wipes away undesired ferromagnetism introduced by cold working in austenitic stainless steel.

The annealing process for stainless steel is typically completed in the mill, and the material is purchased in its annealed form. Austenitics can also be purchased in cold-worked conditions and are commonly referred to as quarter-hard, half-hard, full-hard stainless steels, to name a few.

Case hardening is typically used for applications requiring greater wear resistance, most commonly for industrial food processing (grinders, pelletizers, etc.).

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Ferritic stainless steels, such as 430, have less nickel content than austenitics and comparable amounts of carbon. However, the effect of heat treatment is generally the same. Ferritic stainless components can become more corrosion-resistant as a result of annealing, but thermal processing will not increase its hardness.

There are four primary grades of stainless steel. Austenitic stainless steels, such as 304 and 316, are high-chromium steel grades with the greatest corrosion resistance of all stainless steels. Heat treatment does not increase the hardness of austenitic stainless steel, but it can enhance corrosion resistance and reduce hardness.

Annealing is a controlled heating and cooling process that maximizes corrosion resistance and reduces hardness. It’s the first step in heat treating any stainless steel.

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Cold working manufacturing processes can sometimes introduce ferromagnetism to austenitic stainless steels, which is undesirable for applications such as surgical instruments, medical devices, electronics, and some types of fasteners. Annealing is a common process for these types of parts because it can eliminate the ferromagnetism caused by cold working.