**1. Is A4 70 the same as 316?**
No, they are not the same, but they are very closely related. A4-70 is a grade designation for a **stainless steel bolt, screw, or stud** made from a material equivalent to ASTM 316 stainless steel. The "A4" refers to the steel type (316), and the "70" refers to the bolt's property class (meaning it has a minimum tensile strength of 700 MPa). So, 316 is the **material**, while A4-70 describes a **fastener** made from that material with specific strength properties.
**2. Is A2 steel cold rolled?**
A2 tool steel is most commonly supplied in the **annealed (softened) condition** after being hot rolled. While it is possible to find it in a cold-rolled state, this is not the standard form. Cold rolling is more typical for low-carbon steels sheets and bars where improved surface finish and tighter dimensional tolerances are required. For tool steels like A2, the hot-rolled and annealed form is standard, and the final properties are achieved through heat treatment (hardening and tempering) by the end user.
**3. Is ASTM A36 hot rolled or cold rolled?**
ASTM A36 is most commonly and standardly supplied as **hot rolled**. This is the most economical and widespread process for producing structural shapes, plates, and bars of this grade. While it is technically possible to cold-roll A36 to achieve better surface finish and higher strength, it is not the standard form. When you see A36 steel, you can generally assume it is hot rolled.
**4. Is 4140 harder than A2?**
The answer depends on their heat treatment condition. In their commonly supplied annealed state, A2 tool steel is typically harder than annealed 4140. However, after proper heat treatment (quenching and tempering), **4140 can achieve a higher maximum hardness** (up to ~60 HRC) than A2 (up to ~62 HRC). In practice, A2 is prized for its excellent wear resistance and good hardness, while 4140 is valued for its high strength and toughness. For applications requiring the highest possible hardness, a different steel like D2 or a high-speed steel might be chosen over both.
**5. Will A2 steel rust?**
Yes, A2 steel can rust, but it is more corrosion-resistant than most tool steels that are not stainless. A2 is considered a "semi-stainless" or air-hardening tool steel. It has a moderate chromium content (around 5%) which gives it much better resistance to rust than plain carbon or low-alloy steels (like O1 or 4140). However, it does not have enough chromium (at least 10.5%) to be classified as a true "stainless steel" like 440C or 304. It will develop surface rust or patina if left in a damp or corrosive environment.
