Frequently Asked Questions｜SANYO METAL INDUSTRIES CORP.

Frequently Asked Questions

Q1
What is cold-finished steel bars?

A1
In general, the rod and wire rod that are hot-rolled at a steel manufacturer are called "mill scale materials", and scale remains on the surface. There are also limits to dimensional accuracy (tolerances, roundness) and straightness. Therefore, depending on the customer's usage, it is necessary to improve these issues. By performing secondary processing on the hot-rolled material, polished steel bars with a scale-free glossy surface and higher precision dimensional accuracy and straightness are manufactured. These are collectively called "Cold finished steel bars.
Q2
What types of Cold-finished steel bars are there?

A2
They are classified into three types based on the processing method: "cold drawn finished steel bars (symbol: D)," "cutting (peeling) polished steel bars (symbol: T)," and "grinding polished steel bars (symbol: G)." Among these, "cold drawn polished steel bars (Cold Drawn Steel Bars)" are the most common, with this method being used in over 90% of cases.
Q3
What types of steel bar are manufactured by Sanyo Metall Industry?

A3
Our company specializes in cold-drawn finished steel bars. However, depending on the specifications, we can also work with external manufacturers to handle composite processing of peeled-cold drawing and cold drawing-grinding polished bar steel, so please consult us.
Q4
What are the characteristics of cold-drawn finished steel bars?

A4
After removing the surface scale of the steel bars (wire rod) by shot blasting, it is drawn through a die to the required shape. The features are:
1. It can be processed into complex shapes depending on the die shape.
2. It has good productivity and yield for cutting and grinding, and is cost-effective.
3. Due to plastic deformation, there is less variation and good shape can be obtained.
4. The strength is improved by work hardening during cold drawing.
Q5
What is a drawing bench?

A5
It is a facility that intermittently draws bar steel to manufacture polished bar steel. This method of using this facility is called Bar to Bar.
Q6
What is a combined machine?

A6
It is a facility that continuously draws wire rods to manufacture polished bar steel, also known as a continuous drawing machine. This method of using this facility is called Coil to Bar.
Q7
What is the range of steel types and manufacturing capabilities handled by Sanyo Metal Industries?

A7
Please refer to the "Products" section of our website. For anything else, please contact us.
Q8
What is the minimum order quantity for an order?

A8
The ordering lot for steel materials is based on 2-ton increments, but we can consider continuous orders upon consultation.
Q9
JIS G3108 "General steel for polished steel bars" lists SGD3, but the drawing indicates SGD3-D9. What does "D9" mean?

A9
"D" is the symbol for cold drawing, and "9" is the symbol for dimensional tolerance "IT9". For details on dimensional tolerances, please refer to JIS 3123 "Cold drawn steel bars." The dimensional tolerance for cold-drawn steel is generally "IT9."
Q10
Under what circumstances is heat treatment performed when producing cold-drawn finisheded steel bars?

A10
For large or irregularly shaped products, we perform heat treatment before cold drawing. The type of heat treatment adopted depends on the type and shape of the steel. We generally perform spheroidizing annealing to improve cold-drawing properties or low-temperature annealing to eliminate internal stress.
Q11
What is the meaning of "tempering"

A11
"Tempering" is a heat treatment method performed after quenching, abbreviated as "QT". It increases toughness by returning the martensite structure formed during quenching to a sorbite or troostite structure. Quenching increases hardness (strength) while tempering increases toughness.
Q12
What is the difference between tempered steel and non-tempered steel?

A12
Tempered steel is steel that has undergone the above-mentioned quenching and tempering heat treatment. On the other hand, non-tempered steel is steel that has been given equivalent mechanical properties to tempered steel by adding alloy elements such as vanadium to the composition and generating a fine structure by controlled cooling during hot rolling. However, in terms of toughness, non-tempered steel is slightly inferior to tempered steel.
Q13
What does decarburization mean?

A13
It is a phenomenon in which the carbon on the surface of steel material is released by combining with oxygen in the atmosphere when the material is heated at a high temperature. This reduces the amount of carbon on the surface layer of the steel material, which results in lower strength and hardness of the steel. Additionally, it can cause a decrease in hardenability during the subsequent process of high-frequency quenching. However, the operating technology of Japanese specialty steel manufacturers is excellent, and there is almost no material decarburization. Furthermore, in our heat treatment process, we prevent decarburization by heating in a nitrogen atmosphere.
Q14
Can you provide a "zero decarburization" guarantee?

A14
We can guarantee by completely removing the decarburized layer through material cutting (peeling) and then conducting shot blasting and cold drawing. Please consult with us if necessary.
Q15
What does reduction rate mean?

A15
The reduction rate refers to the percentage decrease in cross-sectional area during cold drawing. It is calculated as the ratio of the difference between the cross-sectional area before and after drawing to the original cross-sectional area. The average reduction rate of our products is 12-15% for round bars. Increasing the reduction rate leads to work hardening and an increase in strength (hardness), which has a positive correlation.
Q16
What is the surface roughness of cold drawn finished steel bars?

A16
It depends on the steel type, diameter, and reduction rate, but generally the surface roughness is around Ra 0.4-0.9. If further improvement of the surface roughness is required, additional processing is possible, so please contact us for more information.
Q17
How is residual stress controlled in cold drawing?

A17
Cold drawing and straightening are plastic forming processes, which leave residual stress inside the material. We have expertise in controlling and managing this residual stress through manufacturing conditions and inspection, depending on how our customers use the product.
Q18
How is surface defects guaranteed?

A18
We have rotating eddy current testing equipment in both of our factories, and we conduct surface defect inspections with this testing equipment based on our customers' requests.
Q19
How deep can surface defects be guaranteed?

A19
We determine the threshold for eddy current testing based on our customers' requests, but we guarantee a minimum depth of up to 0.1 mm.
Q20
Can any shape be produced for special-shaped bars?

A20
For complex shapes, multiple heat treatments and drawing processes are required to shape them. Please contact us for more information.