Japanese SK4 - High Carbon Steel

SK4 steel is a material that has long supported Japanese chefs, used in Western-style kitchen knives that began to become popular after World War II and their introduction into Japan.

Popularized as a Japanese-made steel, SK4 kitchen knives are still popular today because they are both reasonably priced and easy to sharpen.

Classic Japanese kitchen knives are often made of this material and are generally referred to simply as "steel" or "SK steel".

By the way, there is no steel material called "Japanese steel." Apart from being Japanese-made steel, no other information can be obtained when that name is used.

However, in cases where high-priced steels like White Steel or Blue Steel are used, it is often implied by the product name (For example, our White Steel #1 Montanren range.) So, in most cases where a material is labeled as "Japanese steel," it is presumed to be SK4 or a similar hardness and composition.*

This is because some manufacturers fear that the quality of knives will be judged only by the name of the steel material, even though the hardening, molding, and polishing processes have a greater influence on the quality than the material itself. It will generally be up to the manufacturer themselves if they choose to disclose information about what steel composition is being used. It’s important to remember that knives have many steps in their creation that can impact their performance - material composition is only one of those steps, which we get into in the next section. It is a crucial step, but it is one of many.

*Note: Unless manufacturers or craftsmen publicly state otherwise, this is based on sharpening knives labeled as "Japanese steel" from other manufacturers. This rule may not necessarily always apply, so be sure to double check.

Steel material is crucial for indicating a knife's initial performance (amongst many other things related to craftsman ability and more). Below are some comparisons to give you some understanding showing what a particular step of the process does in terms of impacting sharpness, balance and maintainability.

There’s three key pointers in the above chart to focus on.

• Steel Material has a large impact on sharpness and maintainability (ease of sharpening and resistance to rust).

• Apart from sharpness, heat treatment and the sharpening process in knife creation also have a large impact on sharpness.

• Measuring a knife’s strengths is more than just its sharpness. Balance and maintainability also need to be considered.

Based on the above steel mapping chart, SK4 Steel falls in this position on the graph below

Sharpness and affordability - all in one!

Let’s look at the tables below and explore the composition of SK4 Steel more deeply.

Comparing it to Hitachi Metals' White Steel #2, which is widely used for traditional Japanese knives, you’ll notice higher content of elements such as phosphorus and sulfur, which can contribute to brittleness.

However, the carbon content, which determines the hardness (sharpness) of the blade, is 0.9 or higher. Although not mentioned in our chart above, this is higher than some stainless steel knives that see widespread use, such as 6A (0.55-0.65) or 8A (0.7-0.8) stainless steels.